Commelinidae Cyperales. The Poaceae are mostly herbs comprising one of the largest families of flowering plants with about 500 genera and 8,000 species. The stems are round and commonly hollow, at least in the internodes. The leaves are alternate, and commonly 2-ranked, proximally comprising an open sheathing base with overlapping margins, and distally producing a parallel-veined, strap-shaped blade. On the adaxial leaf surface at the junction of the blade and sheath is an often hairy fringe of tissue called a ligule. The basic unit of the inflorescence is called a spikelet typically consisting of a basal pair of minute sterile bracts called glumes and one or more distichously arranged distal florets on an often zigzag extension of the spikelet axis called the rachilla. Each floret is typically embraced by an additional pair of minute chaffy bracts called the lemma and the palea. The florets are unisexual or bisexual and have usually two or three barely recognizable structures called lodicules that may represent a vestigial whorl of perianth that forces the lemma and palea apart during anthesis, thereby facilitating exsertion of the stamens and stigmas. The androecium typically consists of three or occasionally 6 distinct stamens. The gynoecium consists of a single compound pistil of 2 or sometimes 3 carpels, an equal number of styles with feathery stigmas, and a superior ovary with one locule containing a single subapical to basal ovule. The fruit is usually a caryopsis.
Each "thumbnail" image below is linked to a larger photograph.
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Briza minor, quaking grass (Festucoideae). Some of the florets in these three spikelets have the stamens exserted. Festucoid grasses commonly have more than one bisexual floret, and if they have any sterile florets, i.e. those without pistils, they are situated above one or more fertile florets. The florets of the spikelets are generally compressed from side to side rather than from front to back. When the spikelets mature and disintegrate, the glumes mostly remain on the plant. | ||
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Cynodon dactylon, Bermuda grass (Festucoideae). Exserted yellowish stamens and reddish, feathery stigmas are clearly visible in this photo. Pendulous stamens that produce copious, dry, thin-walled pollen and stigmas that are large and feathery are typical of wind pollinated plants and this is the most common mode of pollination among grasses. | ||
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Panicum torridum, kakonakona, (Panicoideae). Note the very small spikelets and orange stamens barely visible in photo. The panicoid grasses typically have small spikelets, commonly consisting of a single staminate or neuter floret at the base of the spikelet and a single bisexual, fertile, terminal floret. At maturity, the entire spikelet separates from the plant as a unit, including the glumes. Any compression of the florets in the spikelet is usually from front to back rather than from side to side. | ||
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Melinus minutiflora, molasses grass. The sterile lemma of each floret has a long awn up to 1.5 cm in length. | ||
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Cenchrus echinatus, sand bur. In this case the florets are enclosed by a cluster of numerous coalescing bristles that are very effective in aiding dispersal of the fruits by tangling in the fur of animals or feathers of birds. | ||
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Sorghum halepense, johnson grass (Panicoideae). Exserted orange stamens and feathery stigmas are readily apparent in this photo. This particular tribe of panicoid grasses typically has the spikelets in pairs along the axis. Both Panicoid and Festucoid grasses typically have a flap of tissue called a ligule at the junction of the blade and sheathing portion of the leaf. In this case (lower photo) the sheathing portion of the leaf has been pulled away from the stem to make the ligule more visible. A fringe of hairs is often associated with the ligule. | ||
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Saccharum officinarum, sugar cane (Panicoideae). Once a very important cash crop in Hawaii, cultivation of sugar cane is no longer economically rewarding. | ||
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Coix lacryma-jobi, Job's tears, (Panicoideae). This maize relative is naturalized in Hawaii and is sometimes cultivated as an ornamental. The pearl-like accessory fruits are sometimes used for lei construction. | ||
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Oryza sativa, rice (Oryzoideae). This species is one of the most important food crops that humans utilize, providing the primary source of starch for a large segment of the world's population. | ||
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bamboo, (Bambusoideae). The bamboos are the only woody members of the grass family. They also combine the most primitive characters occurring within the family, such as florets with six stamens, and tricarpellate pistils. | ||
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Gigantochloa verticillata, bamboo (Bambusoideae). Note the comparatively large spikelet, and florets with six exserted stamens. |
